1. Field of the Invention
The present invention relates to a bonding device capable of bonding an electronic component by heating the electronic component by irradiating laser light from an inside of a bonding head of the bonding device.
2. Description of the Related Art Japanese Patent Number 3195970 discloses a related bonding device using a bonding method in which a transmittable bonding tool is employed and an electronic component is heated by irradiating laser light and thus the electronic component is bonded.
The related bonding device includes a laser heating device that is able to control oscillation and stop of laser light by turning ON and OFF current supply to the laser oscillator. In addition, the related bonding device is also able to control energy intensity of laser light by changing a current value.
Further, in the related bonding device, since laser light is directly irradiated onto an electronic component, the electronic component can be heated rapidly by supplying current having a predetermined value. Further, the component can be simply cooled down by stopping the laser, and thus a particular cooling unit is not necessary. Accordingly, the related bonding device can shorten a bonding time.
FIG. 8 is an explanatory diagram showing a heating theory of the related bonding device. As shown in FIG. 8, laser light 20 passes through an optical fiber 9 connected to a laser oscillator 14 as a light source. The laser light is diffused when exiting from the optical fiber. Thus, even in the method of heating a semiconductor chip 1 as an electronic component by irradiating laser light 20 thereon, the exited laser light 20 is condensed by passing through a condensing lens 11 disposed in an optical path, and the irradiation area is made to coincide with a size of the semiconductor chip 1 in order to use energy for the heat generation effectively.
In the related bonding device, the laser light 20 may be oscillated in a state where a bonding tool does not suck and hold the electronic component at the time of assembly adjustment and the like. In this case, since a focusing point 12 (a point at which a laser diameter is minimized) of the laser light 20 has an extremely powerful energy, a placing stage or a substrate may be damaged and destructed if the focusing point is located on or near the placing stage or the substrate.
Further, in a manufacturing process using the related bonding device, silicon that is frequently used for the semiconductor chip 1 can absorb infrared light as the laser light 20. However, optical absorptance of the silicon is about 60% to 70%, and the rest of the laser light 20 is transmitted through the semiconductor chip 1. Thus, even though a power of the laser light decreases when the laser light is transmitted through the semiconductor chip 1, the laser light 20 is irradiated onto a substrate and the like. In this case, at the focusing point 12, the laser light may still have energy enough to damage or heat the substrate and the like. Moreover, when a bonding process is performed in a state where the substrate is heated and expanded, positions of a bump and an electrode are deviated from each other, and thus the bonded product may become defective.
In the related bonding device, irradiation of the laser light is controlled depending on only a preset current value i and a preset time t as shown in FIG. 9. Thus, since the laser oscillator should be turned ON and OFF repeatedly, there has been a problem of durability of the laser oscillator. Further, some electronic components are not allowed to be rapidly cooled down. For example, if the electronic components are rapidly cooled down, solder is deformed as spots or internal stress occurs therein when the solder solidifies. Hence, stability and position precision of the bonding process deteriorates.
As a heating unit of the bonding device, there has been proposed a heating method (Joule heating system) in which laser light is irradiated onto a bonding tool being absorptively holding an electronic component and the electronic component is heated by the bonding tool. In this heating method, rear temperature is detected by using a thermocouple formed on the bonding tool for holding the electronic component. Therefore, a current value can be feedback-controlled in accordance with a preset temperature profile.
However, in the method of irradiating laser light onto the electronic component, the electronic component is heated by irradiating the laser light directly on the electronic component. Thus, even when temperature of the bonding tool is set, control is independent of the setting. In addition, since temperature of the electronic component can not be directly measured, a current value can not be feedback-controlled. Consequently, the heating method of heating the electronic component by directly irradiating laser light on the electronic component is not suitable for some electronic components which are difficult to be rapidly cooled down.
In addition, the related bonding device disclosed in Japanese Patent Number 3195970 is configured to guide laser light through an optical fiber. However, the optical fiber may be damaged, broken and cut. In such a state, it is difficult to perform a bonding process by appropriately heating an electronic component. In addition, the laser light may leak outside.
JP-A-02-258185 discloses a unit of detecting abnormality of the fiber before the bonding process. Incidentally, in a method of detecting the abnormality of the fiber at the time of bonding (or cutting), detection is performed after the electronic component and the substrate are heated and pressed. However, since a bump and a bonding agent (resin and the like) are deformed after the electronic component and the substrate are heated and pressed, it is difficult to use them again. Therefore, the method of detecting the abnormality of the fiber at the time of bonding (or cutting) is not useful.
The inspection unit disclosed in JP-A-02-258185 is an inspection unit of a laser device used in a laser cutting (used in a cutting process of industrial products or medical treatment). In the inspection unit, inspection light is separately generated from a light source for inspection, independent of a laser cutting, and fiber abnormality is inspected by detecting inspection light exiting from the other end of an optical fiber for the laser cutting.
However, the inspection unit should have an individual light source other than a main light source for a cutting process. Thus, a size of the inspection unit becomes large and complicated.